1. Field Of The Invention
The invention relates to a continuous process for the production of multivalent aryl cyanates from the corresponding phenols and cyanogen chloride.
2. Background Art
Aryl cyanates, the phenol esters of cyanic acid, are important building blocks for synthetic resins (see, e.g., German OS 1,720,663). Usually aryl cyanates are produced from the corresponding phenols and cyanogen chloride, and the hydrogen chloride resulting as by-product is bound by a base as a salt (German AS 1,195,764). Since cyanogen chloride can be viewed as chloride of cyanic acid, this reaction formally corresponds to the production of an ester from the corresponding alcohol and the corresponding acid chloride. But since both cyanogen chloride and the resulting aryl cyanates are highly reactive compounds, precisely defined reaction conditions must be maintained for suppression of secondary and subsequent reactions to obtain satisfactory yields and sufficiently pure products. In particular, in the case of such aryl cyanates, which can be purified neither by distillation nor by crystallization, special significance attaches to the last-mentioned criterion.
The known processes for the production of pure multivalent aryl cyanates (German OS 2,446,004; 2,507,671; 2,507,705; 2,529,486 and 2,529,487) are either discontinuous processes or require an aqueous-organic two-phase system. Furthermore, an excess of cyanogen chloride must often be introduced in the discontinuous processes, which in the case of large batches, also represents a safety risk (cyanogen chloride is very toxic).